In the United States, diabetes mellitus (DM), a major cause of blindness, affects more than 21 million persons. The most common reasons for vision loss in those with DM are cataract and diabetic retinopathy (DR). Success rates of cataract surgery in persons without DM are generally very high. However, in multiple relatively small observational studies, a subset of patients with DM experience progression of DR after cataract surgery and less-favorable outcomes. Given the high costs of resources to monitor and treat cataract and DR (>$5 billion in 1996-2000) and that diagnoses of these conditions will increase as the U.S. population ages, it is important from both patient-care and health-policy perspectives to identify possible risk factors for DR progression after cataract surgery. Analyses using large health care databases can reveal patterns of care and health outcomes for various medical conditions. The proposed study would analyze longitudinal data from such sources to better understand the possible association of cataract surgery with development or progression of DR. Unlike the previous small observational studies on this topic, this project would include thousands of patients with DM undergoing cataract surgery. Furthermore, this type of study costs considerably less than conducting a randomized, controlled trial. This study uses two data sources: (1) the Medicare Current Beneficiaries Survey (1992-2005), a survey with longitudinal data on medical services utilization and costs for a nationally representative sample of more than 12,000 Medicare beneficiaries annually, and (2) the i3 InVision(tm) Data Mart (2004-2007), a large managed-care database with detailed information on more than 24 million covered lives. Using data from these sources on patients with DM who have cataract surgery and age-matched controls with DM and no cataract surgery, we will assess whether cataract surgery is associated with an increased risk for DR onset or progression, use of more resources to monitor and treat DR, or higher costs of care in patients with DM. Last, in a conditional logistic regression, we will examine whether demographic or clinical factors (e.g., poorly controlled blood sugar) are associated with elevated risk for DR or DR progression after cataract surgery. By elucidating risk factors for DR onset and progression after cataract surgery, we could more closely monitor this "high-risk" subset of patients and study early interventions to reduce DR progression and vision loss.